Redes Flexíveis

Since the 2000s, the electric grid has evolved by incorporating increasing levels of intelligence, becoming a “smart grid.” Today, IT-based automated systems and associated field devices work together to manage and integrate energy subsystems (generation, transmission, distribution, and storage).

  

The climate agenda has accelerated the adoption of variable renewable energy (VRE), which is harder to integrate.  The grid must handle intermittent output and bidir flows btw generators and consumers, requiring a “new” power grid.

 

Solar & wind are the new building blocks of tomorrow’s power grid, increasingly replacing synchronous generators, which compromises frequency stability and renders traditional inertia-based response mechanisms (based on energy stored in large rotating machines) & analysis methods insufficient.

  

Grid flexibility concerns the power systems ability to manage changes in supply & demand: many techs contribute to this [DD, 2023]:

  

• Constant REN, such as hydropower.

• Utility-scale storage, including pumped hydro & molten salt.

• Small-scale storage, such as Li-ion batteries.

• Demand-response tools (smart thermostats & appliances) to manage demand peaks.

  

Inverter-based resources - IBR

​

The challenges of operating w/ high shares of inverter-based resources (IBR) in grids with low system strength & low inertia (due to the decreasing presence of sync gens) should be highlighted.  At higher levels of VRE sources (and, consequently, IBR) penetration, new advanced inverter controls, based on grid-forming (GFM) techs, will be needed to maintain the system stability.

​

Grid-edge techs

​

Electricity system is moving away from the centralized paradigm to a decentralized & bidirectional one.  The grid edge (“edge” means the proximity to end-use customers) comprises techs, solutions & business models enabling the transition toward a decentralized & distributed electric grid.  Grid edge techs are important tools to facilitate higher penetrations of renewable energy and to mitigate climate change.

  

Grid edge, the interface btw the grid and the distributed end users, encompasses a wide range of techs & services, from electric vehicles to heat pumps, and solar panels to home batteries.  Grid edge techs enables energy autonomy, unlocks new economic opportunities or manages renewables & DER, and can also support resilience and allow power to be restored more efficiently after natural disasters.  One of the most promising advances of grid edge techs are "microgrids" & "virtual power plants" (VPPs).

  

Microgrids

  

In this grid-shifting context, microgrids has emerged as a viable alternative to conventional utility grids in providing reliable, secure, and sustainable power supply to a group of consumer units (an island, a campus, or a remote community) [CS, 2021].  They are not essentially like “macro” grids: microgrids support smaller loads, serve fewer consumers, and are deployed over smaller areas.

  

A microgrid is a local energy grid that can operate independently or in conjunction with the main power grid.  By providing voltage & frequency support, microgrids can move away from the main grid in the event of failures or emergencies: flexible, they can also inject power into the grid, or even participating in VPPs.

  

Midcrogrids can be classified into grid-tied (fully served by an electric utility) & off-grid (or islanded mode, used in remote environments).  Off-grid microgrids are constructed where there is a need for electricity (rural areas, islands) but no access to a wide-area electrical grid [CS, 2021].  Categorized microgrids also include single or three-phase, low or médium-voltage connected.

  

Another classification has to do with the direction of the current flow: they can be AC (“Alternating Current” - more widespread) & DC (“Direct Current” - w/ higher conversion efficiency & transmission efficiency due to no reactive current) microgrids.  Figure 1 shows a typical microgrid architecture.

  

Mobile microgrids insure reliable power for applications in remote destinations (like oil drilling & mining) or that require mobility and rapid deployment, such as disaster relief efforts.  Containerized mobile microgrids are often a vessel to provide power for members of the community who don’t have power at their homes but may need hours-worth of power for critical medical equipment like oxygen concentrators.

  

Virtual power plant - VPP - the future of clean energy

  

A virtual power plant (VPP) is a cloud-based distributed power plant that aggregates the capacities of heterogeneous distributed energy resources (DER) for the purposes of i) enhancing power generation, ii) trading or selling power on the electricity market, and iii) demand side options for load reduction.  VPPs use an intelligent control system & bidir tech to aggregate energy from networked resources located at multiple sites, bundling together hundreds of discrete power sources into one during peak demand, just like a centralized power plant [MK, 2023].

  

Emerging in the late 1990s, VPPs offer a cost-effective way to integrate large amounts of intermittent RES, replacing conventional plants while providing greater efficiency and flexibility to handle load fluctuations.  Different energy assets can be aggregated into a VPP [ENELX, 2023]:

  

• Flexible load: refers to the management of electricity demand (consumption) to match the supply of electricity.

• Battery storage: enable organizations to allow consumers to use energy stored during periods of low electricity prices or energy stored by renewable energy sources. 

• On-site solar: help to reduce the volume of electricity purchased from the grid; depending on the contract program, excess solar can be exported back to the grid.

• Electric vehicles (EVs): just like batteries, smart EV charging can respond to grid signals and allow EV owners to shift their charging time from high electricity prices periods to low electricity prices.

  

Benefits of VPPs include the ability to deliver peak load electricity or load-following power generation on short notice (obs.: load-following power plants usually run during the day & early evening, and are operated in direct response to changing demand for power supply).

  

According to WoodMac, CPower, Enel, AutoGrid, Voltus (one of only six firms listed in all three categories: Market Interface, VPP Operator, DER Platform) dominate VPP market.  In the U.S., over a quarter of VPPs are in California, which hosts more than the next three states combined (is home of 140 of the 500 VPPs operating in North America).  The four largest VPP managers, which all operate in California, have together accumulated 4,000 MW [UD, 2023].

  

Figure 2 shows the Cpower VPP vision. Figure 3 shows the Voltus VPP platform, which aggregates DERs into VPPs and sells sells energy, ancillary services, and capacity to grid operators, sharing a portion of the revenue with its partners.

  

Microgrid vs VPP

  

Both involve the integration of DERs, the main difference lies in their purpose & operation.  Microgrids are typically designed to provide reliable & resilient power to a specific area, while VPPs are focused on i) reducing costs, ii) providing grid services, and iii) supporting the integration of renewable energy into the grid [EP, 2023].

  

Grid defection

  

Concomitantly, driven by solar, wind & battery systems price drops, and increasing climate-change driven natural disasters, a relatively large number of consumers are considering disconnecting from the grid and investing in their own energy systems to achieve full energy autarky.